1. Field of the Invention
The present invention generally relates to titanium silicide nitride (TiSiN) layers and, more particularly, to a method of forming titanium silicide nitride (TiSiN) layers.
2. Description of the Related Art
In the manufacture of integrated circuits, intermediate or transition layers are often used as metal barrier layers to inhibit the diffusion of metals into an underlying region beneath the barrier layer and/or to enhance adhesion of subsequently formed layers. These underlying regions include transistor gates, capacitor dielectric, semiconductor substrates, metal lines, and many other structures that appear in integrated circuits.
For example, when a transistor gate electrode is formed, a diffusion barrier is typically formed between the gate material (e.g., polysilicon (Si)) and the metal (e.g., tungsten (W), copper (Cu), aluminum (Al)) comprising the electrode. The diffusion barrier inhibits metal diffusion into the gate material. Such metal diffusion is undesirable because it would change the characteristics of the transistor, or render it inoperative. A combination of titanium/titanium silicide nitride (Ti/TiSiN), for example, is often used as the diffusion barrier.
Such diffusion barrier material may also be used in a tungsten metallization process to provide contacts to source and drain regions of a transistor. For example, in a tungsten (W) plug process, a titanium (Ti) layer is deposited on a silicon (Si) substrate. A titanium silicide nitride (TiSiN) layer is then formed upon the titanium (Ti) layer, prior to forming the tungsten (W) plug. In addition to being a barrier material, the titanium silicide nitride (TiSiN) serves two additional functions: 1) prevents chemical attack of the titanium (Ti) by tungsten hexafluoride (WF6) during tungsten (W) deposition; and 2) acts as a glue layer to promote adhesion of the tungsten (W) plug.
The titanium silicide nitride (TiSiN) layer may be formed using a chemical vapor deposition (CVD) process. For example, titanium tetrachloride (TiCl4), ammonia (NH3) and silane (SiH4) may be thermally reacted to form titanium silicide nitride (TiSiN). Alternatively, titanium tetrachloride (TiCl4) and ammonia (NH3) may be thermally reacted to form a titanium nitride (TiN) layer, into which silicon (Si) is subsequently incorporated by treating such layer using a silicon-containing gas (e.g., silane (SiH4)).
However, when a TiCl4-based chemistry is used to form the titanium silicide nitride (TiSiN) layer, reliability problems are encountered. In particular, by-products generated during the titanium nitride (TiN) layer formation may react with the silicon-containing gas, inhibiting the incorporation of silicon (Si) therein, and adversely affecting the adhesion/barrier properties as well as the resistivity of the titanium silicide nitride (TiSiN) layer.
Therefore, there is a need in the art for a method of forming titanium silicide nitride (TiSiN) layers having improved film characteristics.